The XXL Survey L. Active galactic nucleus contamination in galaxy clusters: Detection and cosmological impact

Sunayana Bhargava, Christian Garrel, Elias Koulouridis, Marguerite Pierre, Ivan Valtchanov, Nicolas Cerardi, Ben J. Maughan, Michel Aguena, Christophe Benoist, Cale Baguley, Miriam E. Ramos-Ceja, Christophe Adami, Lucio Chiappetti, Cristian Vignali, Jon P. Willis

Research output: Contribution to journalArticle (Academic Journal)peer-review

3 Citations (Scopus)

Abstract

X-ray observations of galaxy clusters are impacted by the presence of active galactic nuclei (AGNs) in a manner that is challenging to quantify, leading to biases in the detection and measurement of cluster properties for both astrophysics and cosmological applications. We detect and characterise clusters contaminated by central AGNs within the XXL survey footprint and provide a systematic assessment of the cosmological impact of such systems in X-ray cluster samples. We introduce a new automated class for AGN-contaminated (AC) clusters in the XXL source detection pipeline. The majority of these systems are otherwise missed by current X-ray cluster-detection methods. The AC selection is also effective in distinguishing AGN and cool-core presence using supplementary optical and infrared information. We present 33 AC objects, including 25 clusters in the redshift range, $0.14 \leq z \leq 1.03$, and eight other sources with significantly peaked central profiles. Six of these are new confirmed clusters. We computed the missed fraction of the XXL survey, which is defined as the fraction of genuine clusters that are undetected due to their centrally peaked X-ray profiles. We report seven undetected AC clusters above $z > 0.6$, in the range where X-ray cluster detection efficiency drops significantly. The missed fraction is estimated to be at the level of $5\%$ for the 50 square-degree XXL area. The impact on cosmological estimates from missed clusters is negligible for XXL, but it produces a tension of $\sim 3\sigma$ with the fiducial cosmology when considering larger survey areas. Looking towards surveys such as eROSITA and \textit{Athena}, larger areas and increased sensitivity will significantly enhance cluster detection, and therefore robust methods for characterising AGN contamination will be crucial for precise cluster cosmology, particularly in the redshift $z > 1$ regime.
Original languageEnglish
Article numberA92
Number of pages24
JournalAstronomy and Astrophysics
Volume673
DOIs
Publication statusPublished - 12 May 2023

Bibliographical note

Funding Information:
This work was supported by the Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES. B.J.M. acknowledges support from STFC grant ST/V000454/1. This work was based in part on observations made at Observatoire de Haute Provence (CNRS), France, with the MISTRAL instrument. This research has made use of the MISTRAL database, based on observations made at Observatoire de Haute Provence (CNRS), France, with the MISTRAL spectro-imager, and operated at CeSAM (LAM), Marseille, France

Funding Information:
XXL is an international project based around an XMM Very Large Programme surveying two 25 deg extragalactic fields at a depth of ∼6 × 10 erg cm s in the [0.5−2] keV band for point-like sources. The XXL website is http://irfu.cea.fr/xxl . The authors would like to thank the anonymous referee for instructive comments that helped improve the manuscript considerably. The Saclay team (S.B., M.P., N.C.) acknowledges long term support from the Centre National d’Etudes Spatiales (CNES). S.B. acknowledges a CNES postdoc and support from CNRS, support from the ESA Archival Research Visitor Programme, and would like to thank P. A. Giles, A. Pellissier, J. B. Melin, and R. T. Duffy for fruitful comments. This work was supported by the Programme National Cosmology et Galaxies (PNCG) of CNRS/INSU with INP and IN2P3, co-funded by CEA and CNES. B.J.M. acknowledges support from STFC grant ST/V000454/1. This work was based in part on observations made at Observatoire de Haute Provence (CNRS), France, with the MISTRAL instrument. This research has made use of the MISTRAL database, based on observations made at Observatoire de Haute Provence (CNRS), France, with the MISTRAL spectro-imager, and operated at CeSAM (LAM), Marseille, France. This research made use of ASTROPY ( http://www.astropy.org ), a community-developed core Python package for astronomy (Astropy Collaboration 2013, 2018). This work also made use of the PYPROFFIT package (Eckert et al. 2020), as well as NUMPY , SCIPY and MATPLOTLIB . The data underlying this study are available in the article. 2 −15 −2 −1

Publisher Copyright:
© The Authors 2023.

Keywords

  • astro-ph.CO
  • astro-ph.GA
  • astro-ph.HE

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